In many situations affecting fetal, pediatric and adult patients, existing tools and techniques for repairing structures inside the heart result in suboptimal interventional timing and approach. While catheter-based techniques have transformed the treatment of certain conditions, the breakdown of traditional manufacturing methods at the millimeter and sub-millimeter scale has placed severe limitations on the complexity of catheter-delivered instruments and consequently on their utility. In contrast, open surgical procedures permit complex reconstruction and patient-tailored repairs, however, they involve substantial trauma and risk. What is needed is an instrument technology which combines the limited collateral tissue damage of a minimally invasive procedure with the dexterity and custom fit afforded by the open surgical approach. We propose to develop such a technology by mounting tools and implants constructed using 3D microelectromechanical systems (MEMS) technology on the tips of high-precision steerable needles. Constructed from the concentric combination of curved superelastic tubes, these needles will be able to snake their way through the heart's chambers to a surgical site. And unlike traditional MEMS devices, the EFAB MEMS process we will use will allow us to construct fully-assembled complex millimeter-scale mechanisms from metals which can be removed from their substrate for needle mounting. Control wires to power the tools can be run through the needle's lumen similar to existing handheld and robotic minimally invasive instruments. Three-dimensional MEMS technology has the potential to revolutionize the design of minimally invasive tools and implants. The versatility of 3D MEMS devices is likely to enable new minimally invasive procedures and to improve the precision of current procedures. Using port access, the steerable needles will provide a highly precise platform for positioning the tools within the heart and will be stiff enough to apply the forces necessary to manipulate the tissue. The complexity of this problem is well suited to a BRP. The PI has assembled a multidisciplinary team and established a unique partnership among industry-based engineers (Microfabrica), clinical investigators (Children's Hospital, Boston) and university-based engineers (Boston University). Together, we will develop this technology by addressing the following specific aims: Aim 1 - Develop Steerable MEMS Instruments for Pediatric / Adult Intracardiac Tissue Removal. Aim 2 - Develop Steerable MEMS Instruments for Pediatric / Adult Intracardiac Tissue Approximation. Aim 3 - Develop a Steerable MEMS Instrument for Fetal Intracardiac Tissue Removal.